1. Field of the Invention
This invention relates to ice condenser containments for condensing steam generated from the primary water of a nuclear reactor in the event of an accidental loss of coolant and, more particularly, to a method and apparatus for servicing such ice condenser containments to permit replacing ice which has sublimated and thus been lost from within the ice condenser container.
2. State of the Prior Art
Ice condenser containments are known for employment with nuclear reactors for condensing the steam from the primary water of the reactor in the event of an accidental loss of coolant. In a typical installation, there are provided approximately 2,000 ice baskets, each of which is approximately one foot in diameter and 50 feet in height and is filled with approximately 1,500 pounds of ice. The sidewalls of the ice basket are substantially cylindrical in configuration and are perforated to permit rapid exposure of the steam to the ice and thus to achieve corresponding, rapid condensation.
A problem has developed in the use of such ice condenser containments, in that due to sublimation of the ice, the initial volume and weight decreases with time and thus the lost ice must be replenished, or replaced. A minimum required amount of ice is typically at least 1,200 pounds for each ice basket, for assuring its effectiveness for counteracting the accidental loss of coolant, as above referenced. When the loss due to sublimation reduces the remaining amount of ice to below this minimum, serious safety hazards can be presented.
The structure of the ice baskets, however, has imposed serious obstacles to efficient and effective replenishing of the ice to meet the design standards. This can be more readily appreciated from the simplified schematic illustration of an ice basket 10 shown in FIG. 1. More particularly, FIG. 1 is an elevational cross-sectional view of an individual ice basket 10; as before noted, the ice basket 10 includes a sidewall 12 of generally cylindrical configuration, approximately 50 feet in height and approximately one foot in diameter. Cruciforms 14 are positioned at approximately six foot intervals along the axial height of the basket 10. The cruciforms 14 each comprise a number of metal straps, each approximately 1/8 inch thick and typically 11/2 inches in height, which are integrally joined together at first ends along the axis of the cylindrical ice basket 10 and extend radially thereform to engage the interior sidewalls of the basket 10, to which they are secured as by welding. Typically, each cruciform comprises four such radially extending straps in quadrature relationship and thus equiangularly displaced in 90.degree. intervals, defining an "X"-shaped configuration. The cruciforms intially were provided to afford increased lateral support for the ice basket 10 as a precaution against severe seismic disturbances; however, it has been determined subsequently that such welded-in-place cruciforms are not necessary to maintaining adequate lateral support and that alternative structures, instead, may be employed.
The cruciforms, however, have imposed a substantial obstacle to replenishing the supply of ice, as the latter is depleted due to sublimation. For example, as seen in FIG. 1, the successively lower compartments contain inadequate charges of ice due to sublimation loss, and remain spaced apart due to the presence of cruciforms 14. Thus, while access may be had to the upper, open end of the ice basket 10 for recharging the first and possibly the second upper compartments, the lower compartments are inaccessible, imposing a serious obstacle to achieving the required replenishing of the charges of ice therein. Particularly, the replenishing of the ice charges has been both an arduous and time consuming task and very expensive, not only in performing the required ice recharging function, but also due to the resulting down time of the nuclear reactor and thus its loss of productive power generating time.